The present invention is generally concerned with lined composite can construction, and more particularly with the construction of composite cans in a manner so as to accommodate a reduced internal pressure or an internal vacuum environment.
Substantial advantages of both an economic and environmental nature reside in the use of composite containers as opposed to the more traditional glass and metal containers. Such advantages include reduced expenses both in the materials used and in the procedures involved in the manufacture of the container. Also, and of particular significance, is the fact that composite containers are, to a large extent, biodegradeable and easily disposed of without adversely affecting the environment. However, the use of composite containers is, to an appreciable degree, limited because of the lack of inherent strength in such containers.
A particular area of difficulty is the packaging of products which either inherently produce or require the formation of an internal vacuum environment. As a specific example, in the hot filling of lined composite containers of conventional construction with single strength juice, such as orange, grapefruit and grape juices, there is a substantial likelihood of the cans imploding. The hot filling of these juices into the containers involves direct introduction of the juice from the pasteurizing apparatus into the cans at a liquid temperature of from 190.degree. to 200.degree. Farenheit. After filling, the tops are applied and seamed to the cans and the cans subsequently cooled to less than 100.degree. Farenheit. This cooling creates an internal vacuum of approximately 15 inches of mercury. The pressure differential created by the vacuum environment formed within the can in turn give rise to a very substantial likelihood the can or container will implode. At the very least, air under the higher external or ambient pressure will seep through the fibrous body of the can and act directly against the inner hermetic foil liner. This pressure against the liner, even when provided with a kraft paper backing, will cause a tearing of the liner away from the fibrous body, resulting in an uncontrolled inward blistering, or in fact rupturing, of the liner.
A further discussion of the desirability of the use of composite cans, the problems inherent therein when dealing with vacuum packaging, and one solution for the accommodation of vacuum packaging in composite cans, will be found in Applicant's prior U.S. Pat. No. 4,158,425, the disclosure of which is incorporated herein by reference.